The present invention relates to an aerial photograph image pickup method and an aerial photograph image pickup apparatus by a small type Unmanned Aerial Vehicle (UAV).
In a photographing operation from the air above or a surveying from the air above, information which cannot be acquired by the photographing operation from the ground or by the surveying on the ground can be acquired, and the photographing operation is possible in an off-limits area, or the information in an area where the surveying is difficult can be acquired. Further, in recent years, by the improvement in performance of a small type flying object as remote controlled such as a tiny plane or a small-scale helicopter, etc. and also, by the improvement in a remote control technology, and further, the improvement in performance of an image pickup device, the promotion of the miniaturization, and others, the image pickup device can be mounted in a small flying object. By remotely controlling the flying object, the photographing operation from the air above can be performed in an unmanned manner.
Further, it is also possible to perform autonomous flight according to a flight schedule as set up in advance. By setting three-dimensional position for taking aerial photograph in advance, it is possible to acquire still images from a predetermined position. Also, digital photogrammetry can be performed from the still images.
On the other hand, in a case where the photographing operation is performed by a small flying object, it is desirable that the helicopter body is in horizontal posture. In fact, however, the helicopter body is often tilted because the helicopter body is light in weight, and the body is often swept away by the wind. Therefore, in a fixedly mounted image pickup device, an optical axis is tilted depending on a state of the body, and a tilt direction may not be constantly fixed.
In case of preparing an image in wide range, or in case of preparing a stereoscopic image, two images adjacent to each other are overlapped, connecting points (tie points) common to the two images are extracted in the overlapped portions, and the images are combined by using the tie points as reference.
However, as described above, when the images taken in a state that an optical axis is tilted and a tilt angle or a tilt direction is not fixed are sequentially combined with each other, a resultant image in the extensive range which can be acquired is distored or curved and there is a problem that a correct combined image cannot be obtained. Also, distortion or curving of the image may exert influence on the accuracy of the digital photogrammetry.